Information pertaining to Qadha Salaah

As-Salaam-U-Alakum Mufti,We are aware of the origin of Salaah & that we must read it on time. Please advise the origin of reading Khazaah Salaah, when one misses the time of Salaah & where can we read more about Kazaah Salaah.Shukraan & Was-Salaam.